Conventionally, there have been proposals of technologies for bed devices whose legs are adjustable in length.
For example, Japanese Patent Application Laid-open 2006-136669 (which will be referred to hereinbelow as “Patent Document 1”) discloses a mattress that is adjustable in bottom length by making the foot-side part of the mattress expandable and contractible in the longitudinal direction of the bed device. In this Patent Document 1, the mattress put on the bottom of the bed is formed of a monolayer urethane foam core in which, in order to adjust the degree of repulsion in the foot side part, cross-shaped or linear shaped through-holes are punched in the thickness direction at regular intervals in a staggered layout.
On the other hand, Japanese Patent Application Laid-open 2009-273894 (which will be referred to hereinbelow as “Patent Document 2”) discloses a configuration in which, as shown in the drawings, the foam core of the mattress is formed with corrugation in the foot section. In this case, the corrugation of the foam core allows the foot section to diminish in length when the foot section of the deck is contracted in length.